Recent research at the U.S. Department of Agriculture (www.hbci.com/˜wenonah/new/pnutskin.htm) have brought attention into the potential use of lignoceric acid as an ingredient in dermal oils and creams and hair conditioners, due to its excellent properties as a moisturizing and softening agent when used in said products. Currently, behenic acid is used for the same functions and is commercially available, which is not the case for lignoceric acid. Researchers consider that a mixture of both fatty acids could have higher moisturizing properties than those of behenic acid alone. The USDA researcher's interest arose from the discovery of the presence of both behenic acid and lignoceric acid in the thin skin that coats peanut seeds, which they consider could become a potential source for the commercial production of lignoceric acid, currently inexistent.
In fact, lignoceric acid is only found in trace amounts in the majority of the vegetable oils, with the exception of peanut oil (1%). It is contained in higher amounts in sources with no commercial production, such as oil from the seeds of the red sandalwood tree (Adenanthera pavonina), a leguminous tree (up to 25%), or in commercially available sources that are very valuable by themselves and do not warrant their processing to obtain lignoceric acid, such as e.g. carnauba wax (30%) and rice bran wax (40%). A potential source that could be eventually used for production of lignoceric acid is the thin skin that coats peanut seeds, as mentioned before.
Currently, no process is known to recover lignoceric acid at a commercial scale from any of the previously mentioned sources for the purpose of application in large scale products and no providers are available, excepting companies selling laboratory analyticals or fine chemicals, such as e.g. Sigma Chemicals, US$ 515/10 g (99%).
Another possible commercial source of lignoceric acid is black liquor soaps. These are residues of the sulfate process or Kraft pulping of pine wood for the production of cellulose and fundamentally comprise sodium salts of fatty acids, among them lignoceric acid, salts of rosin acids, a complex series of non-saponifiable materials and dark degradation products such as lignin. The solid content of black liquor soaps ranges from 40 to 70% by weight. The black liquor is acidified with sulfuric acid to convert it into “tall oil”, which is used as a source for obtaining fatty acids and distilled rosin acids used in the manufacture of esters, alkidic resins and the like. Since the color of tall oil influences the quality of the obtained products, several processes have been developed for their refining, i.e. for removing compounds responsible for the color of tall oil.
One of the earliest of such color removing processes is disclosed in the U.S. Pat. No. 2,519,903, filed on Aug. 22, 1950 and entitled “Removal of the sodium salt of lignoceric acid and other materials from a tall oil soap”. The disclosed process essentially consists in diluting black liquor soaps with water to a solid content ranging from 0.5 to 25% in weight, and letting the dilution to settle during at least one hour. A large part of the colored compounds are among the decanted solids, together with the sodium salt of lignoceric acid, or sodium lignocerate. Although only the refining process is claimed, processes for recovering lignoceric acid, which can amount up to 1.4% by weight of the solids in the black liquor according to the authors, are also disclosed.
However, the disclosed refining process has never been implemented commercially, partly due to the costs associated to the large dilution of the solids, high energy consumption for the recovery of sodium sulfate through evaporation of large volumes of water, and finally the development of better and more efficient processes for the refining of tall oil. Nevertheless, in view of the objectives of the present invention, the process disclosed in the U.S. Pat. No. 2,519,903 constitutes the closest prior art to the present invention, as far as there are no other processes in the state of art for the production of lignoceric acid for large scale applications.
The objective of the present invention is to provide a novel process for the production of lignoceric acid, which is easy to implement at a commercial scale and is able to produce lignoceric acid at a cost compatible for bulk utilization and application in large scale products such as cosmetic creams and lotions and the like.
The process of the invention that is described in the following paragraphs is illustrated by nine examples and one figure (FIG. 1) and fulfills the abovementioned objective. It consists of a catalytic oxidation step of a raw material that comprises lignoceric alcohol, followed by a series of other physical and chemical steps that interact synergistically between them to yield lignoceric acid. The entire process as well as each of its steps has been developed or adapted according to the nature of the raw material, intermediate products and the final product, and constitutes an invention with no antecedents in the state of the art, which is also not obvious for someone skilled in the art. For the purpose of this invention, the raw material can be a material composition with a content of at least 50% by weight of lignoceric alcohol, and the process of the invention comprises eight chemical and physical steps consisting of:                a) forming a reactant mixture by contacting the raw material, quaternary ammonium peroxotunsgtophosphate and an aqueous solution of hydrogen peroxide during a time interval sufficient to form a reacted mixture comprising lignoceric acid;        b) separating the reacted mixture from step (a) into an aqueous phase and an organic phase, wherein the organic phase comprises lignoceric acid;        c) forming a saponifying mixture by contacting the organic phase from step (b) with an aqueous solution of one or more alkaline metal hydroxides, where the alkaline metal hydroxides can be selected from the group consisting of sodium hydroxide or potassium hydroxide, heating the mixture to a temperature of at least 90° C. and keeping said temperature during a time interval sufficient to form a saponified mixture comprising the lignocerate;        d) evaporating the saponified mixture from step (c) to obtain a residue comprising the lignocerate, wherein said residue has a water content of at most 1% by weight based on the total residue weight;        e) distilling the residue from step (d) at a temperature ranging from 200° C. to 350° C. and at a pressure of less than 60 mbar to obtain a distillate and a solid residue, wherein the residue comprises the lignocerate;        f) forming a mixture by contacting the solid residue from step (e) with an aqueous solution containing one or more acids selected from the group consisting of acetic acid, hydrochloric acid and sulfuric acid, heating the residue and the solution mixture up to a temperature between 90° C. and 150° C. during a time interval sufficient to form a liquid mixture comprising lignoceric acid;        g) cooling the liquid mixture from step (f) down to at least room temperature or less, and keeping said temperature during a time interval sufficient to form a liquid phase and a solid phase, wherein the solid phase comprises the lignoceric acid; and        h) separating the solid phase from step (g) from the liquid phase, wherein the solid phase comprises the lignoceric acid.        
Lignoceric alcohol or tetracosanol is a convenient raw material, since it is relatively abundant in many readily available sources, such as some plant waxes, e.g. sugar cane wax, aliphatic alcohols derived from tall oil or mixtures of industrial synthetic fatty alcohols obtained through oxidation of paraffins. All of these are abundant and convenient sources to obtain lignoceric alcohol.